Harmonic Disturbance Rejection Control for Magnetic Field Compensation Applications

A simple control strategy was studied for harmonic disturbance rejection in magnetic field compensation systems for low-field magnetic resonance techniques. The strategy is based on the simultaneous action of a conventional PID and a selective harmonic-compensation controllers. The system consists of a set of compensating coils fed by independent current sources driven by a digital controller. A series of hall magnetic sensors close the control loop. Despite its simplicity, it is shown that the performance of the dual controller improves within the frequency range where the waterbed effect becomes dominant, by selectively enhancing the rejection of the harmonic component. The proposed solution is particularly useful for selective harmonic rejection of slowly varying frequency and amplitude dependent harmonic perturbations. An extension to multiple-harmonic components perturbations is possible.Fil: Forte, Guillermo Omar. Universidad de Cordoba. Fac. de Matemática Astronomía y Física; ArgentinaFil: Anoardo, Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Conicet - Cordoba. Instituto de Fisica Enrique Gaviola; Argentin

Longitudinal gradient-coil with improved uniformity within the volume of interest

Ponencia presentada en la 2014 IEEE Biennial Congress of Argentina (ARGENCON), 11 - 13 Junio de 2014, San Carlos de Bariloche, Argentina.We present a longitudinal magnetic fieldgradient-coil with optimized uniformity within the volume ofinterest (VOI). The accuracy of the optimization algorithm wasconfronted with measurements of the spatial dependence of themagnetic field within the VOI in a prototype-coil. Theproposed device integrates the gradient-unit of a fast-fieldcyclingmagnetic resonance imaging (MRI) apparatus of owndesign.Se presenta una bobina de gradiente de campo magnético longitudinal con uniformidad optimizada dentro del volumen de interés (VOI). La precisión del algoritmo de optimización es cotejada con mediciones de la dependencia espacial del campo magnético en un prototipo. Este dispositivo integra la unidad de gradientes de un aparato de imágenes por resonancia magnética (IRM) con ciclado rápido de campo de diseño propio.Fil: Domínguez, Gabriela Alejandra. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física. Laboratorio de Relaxometría y Técnicas Especiales; Argentina.Fil: Domínguez, Gabriela Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina.Fil: Romero, Agustín. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física. Laboratorio de Relaxometría y Técnicas Especiales; Argentina.Fil: Romero, Agustín. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina.Fil: Anoardo, Esteban. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física. Laboratorio de Relaxometría y Técnicas Especiales; Argentina.Fil: Anoardo, Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina.Física Atómica, Molecular y Química (física de átomos y moléculas incluyendo colisión, interacción con radiación, resonancia magnética, Moessbauer Efecto.

Using Proton Nuclear Magnetic Resonance (NMR) as a calibrating reference for magnetic field measurement instruments: Sensitive volume and magnetic field homogeneity

Nuclear magnetic resonance can be conveniently used to set up reference values of magnetic flux densities for the calibration of measurement instrumentation. Two measurement procedures are proposed based on the Fourier analysis of the nuclear magnetic signal. Particularly, we consider the situation where the reference magnetic flux density may change its value across the sensor active area/volume due to spatial inhomogeneities. An explored potential solution uses an electronic compensation system in order to minimize the spatial inhomogeneities of the magnetic flux density within the calibrating volume. For this purpose, a previously designed device was added to the magnetic resonance apparatus. Both methods allow a performance better than 10 ppm in calibrating measurements by using a magnetic flux density source of the order of 100 ppm in spatial homogeneity within the calibrating volume. Examples of both methods are discussed.Fil: Rodriguez, Gonzalo Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Forte, Guillermo Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Trovintek Advanced Magnetic Systems; ArgentinaFil: Anoardo, Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Trovintek Advanced Magnetic Systems; Argentin

A fast field-cycling MRI relaxometer for physical contrasts design and pre-clinical studies in small animals

We present a fast field-cycling NMR relaxometer with added magnetic resonance imaging capabilities. The instrument operates at a maximum proton Larmor frequency of 5 MHz for a sample volume of 35 mL. The magnetic field homogeneity across the sample is 1400 ppm. The main field is generated with a notch-coil electromagnet of own design, fed with a current whose stability is 220 ppm. We show that images of reasonable quality can still be produced under such conditions. The machine is being designed for concept testing of the involved instrumentation and specific contrast agents aimed for field-cycling magnetic resonance imaging applications. The general performance of the prototype was tested through localized relaxometry experiments, T1-dispersion weighted images, temperature maps and T1-weighted images at different magnetic field intensities. We introduce the concept of positive and negative contrast depending on the use of pre-polarized or non-polarized sequences. The system is being improved for pre-clinical studies in small animals.Fil: Romero, Javier Agustin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Universidad Nacional de Córdoba; Grupo de Resonancia Magnética Nuclear; Laboratorio de Relaxometría y Técnicas Especiales (LaRTE); ArgentinaFil: Rodriguez, Gonzalo Gabriel. Universidad Nacional de Córdoba; Grupo de Resonancia Magnética Nuclear; Laboratorio de Relaxometría y Técnicas Especiales (LaRTE); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Anoardo, Esteban. Universidad Nacional de Córdoba; Grupo de Resonancia Magnética Nuclear; Laboratorio de Relaxometría y Técnicas Especiales (LaRTE); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentin

Desarrollo de electroimanes reconfigurables para uso en resonancia magnética nuclear y metrología magnética

Una técnica experimental de creciente interés en la comunidad internacional es la relaxometría magnética nuclear, la cual posee un amplio campo de aplicabilidad en la industria farmacéutica, alimentaria, petrofísica, caucho, cosmética y plástico, entre otras. Actualmente se desarrolla en el LaRTE (Laboratorio de Relaxometría y Técnicas Especiales) un prototipo alfa de un instrumento unico de resonancia magnética nuclear con campo magnético ciclado, que permitirá no solamente realizar estudios relaxométricos en muestras de hasta 35cm3, sino que posibilitará la obtención de imágenes y mediciones de difusión a diferentes valores de campo. El corazón de este aparato es un electroimán particular logrado con tecnología propia, el cual posee excelentes características al compararlo con el estado del arte. Este logro da sustento al desarrollo en marcha, el cual será posiblemente transferido a una empresa espín-off del laboratorio (Trovintek Advanced Magnetic Systems) en el futuro para un desarrollo beta. En esta dirección, este proyecto propone profundizar el desarrollo de los imanes logrados, tratando de alcanzar sistemas reconfigurables adaptivos según las características del campo requerido y según demande la aplicación (homogeneidad, velocidad de conmutación e intensidad). A su vez, estos mismos sistemas de imanes prometen excelente aplicabilidad en el campo de la metrología magnética, dirección en la cual el LaRTE ya ha comenzado a trabajar conjuntamente con la Unidad Técnica Electrónica del INTI (Córdoba). Dichos electroimanes pueden devenir, en si mismos, en dispositivos especialmente diseñados para tal aplicación

Field-cycling NMR detection of magnetoacoustically manipulated nematic ordered states: Memory effects

The proton spin-lattice relaxation time (T1) dispersion was studied under simultaneous sonication in the nematic phase of 5CB. It appears that metastable ordered states subject to a memory effect can be induced by the combined action of an amplitude-modulated ultrasonication and a pulsed magnetic field. We argue that the acoustic amplitude modulation adds instability to the nematic phase through director order fluctuation enhancement. Different manipulated states of the director were unambiguously identified by the Larmor frequency dispersion of T1. The field-cycling NMR technique was used for T1 measurements. © 2007 Elsevier B.V. All rights reserved.Fil: Anoardo, Esteban. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Kimmich, R.. Universitat Ulm; Alemani

Proton double irradiation field-cycling nuclear magnetic resonance imaging: Testing new concepts and calibration methods

Double resonance experiments in field-cycling nuclear magnetic resonance (NMR) are powerful tools for the indirect detection of quadrupolar and electron resonances, dynamic nuclear polarization-induced signal amplification, within other possibilities. In the context of magnetic resonance imaging, double irradiation at high and low magnetic fields in field-cycling experiments can be conveniently used for instrumental calibration purposes and contrast manipulation. The basic goal of this article is to present a practical method for the measurement and calibration of the magnetic field in field-cycling magnetic resonance imaging instruments using proton resonances at high and low fields. We discuss an experimental protocol to adjust the optimal position of the gradient unit respect to the sample and the magnet system, and to measure the effective magnetic field gradient across the sample. A new modality of slice selection by irradiating the sample in the presence of a gradient field at low magnet-field conditions is also discussed. As a practical matter, we show how the sample irradiation at low fields can be used for contrast-enhancement, while handling the NMR signal intensity with spatial selectivity. To the best of our knowledge, this is the first calibration and adjustment package for a field-cycled magnetic resonance imaging instrument and the first example of double irradiation direct manipulation of contrasts in a proton image.Fil: Rodriguez, Gonzalo Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Anoardo, Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentin

New challenges and opportunities for low-field MRI

In this manuscript we deal with recent advances in low-field Magnetic Resonance Imaging (MRI). The development of low-cost MRI solutions allowing portability and trustable diagnosis is a hot topic worldwide by these days. We analyze basic technical issues of recent examples of fixed-field instruments operating at low-field. Then we discuss pros and cons of the pre-polarized approach, from both physical and technical perspectives. Permanent magnet and electromagnet technology are confronted. Finally, magnetic field-cycling is introduced as an alternative MRI technique, where field-dependent experiments can be exploded for the development of new contrast mechanisms that are not feasible for fixed-field MRI instruments. As field cycled machines usually deals with switched currents in electromagnets, magnetic field instability and inhomogeneity are the main limiting factors affecting image quality. We finalize this manuscript discussing how it turns possible to overcome these limitations, thus opening new possibilities for the development of cost effective MRI technology

Dynamical regimes of lipids in additivated liposomes with enhanced elasticity: A field-cycling NMR relaxometry approach

We study the molecular dynamics of lipids in binary large unilamellar liposomes suspended in D2O composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) or soy phosphatidylcholine (SPC) additivated with different percentiles of sodium deoxycholate (SDC). We use the fast field-cycling proton NMR relaxometry technique over a wide timescale and at diverse temperatures. A model previously validated in different formulations is here employed for the relaxometric analysis of elastic vesicles. A new dynamical regime is observed for the first time in additivated DMPC and additivated/non-additivated SPC liposomes. This surprising feature is discussed in terms of vesicle shape fluctuations, enhanced elasticity and lipid & additive diffusion within the membrane. The continuum elastic theory is revisited for a better understanding of recent experiments and those here presented. We address the point of deformability measurements across rigid permeable barriers versus measurements of the bending elastic modulus in free-standing vesicles.Fil: Fraenza, Carla Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Anoardo, Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentin